1. Field of the Invention
The present invention relates to direct access storage devices such as disk drive units which have a transducer head positioned over a magnetic medium. More specifically, the present invention relates to systems and techniques for predicting failure in direct access storage devices.
2. Description of the Related Art
Direct access storage devices such as disk drive provide memory storage for computers and other data processing and communication systems. The disk drives units typically include a rigid disk on which a magnetic medium is provided. A protective overcoat is applied to the magnetic medium which is typically carbon or zirconia with a thin coating of liquid or solid lubricant such as polyperfluoroether.
Data is written to and read from the medium by a transducer which flies over the disk on a cushion of air referred to as an "air bearing". The air bearing is created by a high speed rotation of the disk. Thus, notwithstanding the lubricant applied to the disk, air is the primary lubricant while the transducer is flying. A slider supports one or more transducer heads on an arm suspended from a pivot point over the disk. At the high rotation rates of conventional drives, failure of the slider to maintain head-disk separation can result in a catastrophic head disk interaction (HDI) or "head crash". While an HDI was once thought of as an instantaneous event, currently, it is recognized as a sequence of events. For example, the system may start off with the slider flying or in limited contact. If the slider then picks up some debris, the debris will either drag over the disk or alter the air bearing such that the slider flies lower. Debris may continue to collect on the slider as it flies at lower and lower spacings. Eventually, the slider begins to contact the disk initially using up the liquid or solid lubricant, wearing through the carbon overcoat and damaging the magnetic medium. This will roughen the disk surface making even partial flying over the affected tracks improbable. This is the HDI condition by which data can not be read or the servo-system fails.
Failure of a head disk assembly (HDA) from a head disk interaction frequently involves a loss of data. In some cases, the data can not be recovered. Thus, there has been a need in the art for systems and methods for predicting impending head crashes in disk drives.
One conventional technique for detecting an impending failure of a disk drive involves the use of external instruments to measure wear on the disk. This is an expensive process which necessitates an interruption of the operation of the system.
Another technique involves the use of a piezoelectric sensor mounted on the disk drive head to sense a change in friction between drive head and the medium and to generate a warning when the change in friction exceeds a predetermined level. However, this requires a costly addition of a separate piezo-electric sensor into the drive. In addition, the additional sensor may interfere with the operation of the system and increase system complexity.
Thus, a need remains in the art for an inexpensive system and technique for predicting impending head crashes which does not require an interruption in the operation of the system, external hardware or the costly addition of internal components.